A color filter used in a liquid crystal color display or the like generally has a colored pixel part (array), formed on a transparent substrate such as glass and corresponding to three primary colors, namely, red (R), green (G), and blue (B). The methods of manufacturing the colored pixel array may include the following four types: dyeing, pigment dispersion, printing, and electro-deposition. Among these four methods, the pigment dispersion method is excellent in terms of performance and production costs. Therefore, the pigment dispersion method is widely used today, and is expected to remain dominant in the future.
In the pigment dispersion method, a color resist is applied to the surface of a substrate using a spin coater or dye coater, and the color resist layer is patterned using, for example, a photolithography technique. This process is repeated for each color in due order (e.g., for R, G, and B in this order) to form a three-color (RGB) pixel array. In this case, the second-applied color resist (e.g., G) is affected by the first-applied color resist pattern (e.g., R) to make the thickness of the second color resist uneven (that is, to cause uneven application). Similarly, the third color resist (e.g., B) is affected by the underlying two-color resist patterns to make the thickness of the third color resist uneven. Since the thickness of each color resist layer may affect the spectral characteristics of light, it is desirable that the thickness of each color resist layer be made as uniform as possible.
An overcoat layer is applied to, or coated over, the surface of the colored pixel array as a protective layer using the coater in the same manner as those of the color resist layers. The surface of the overcoat layer needs to be as flat as possible. This is because, if the surface of the overcoat layer is not flat (that is, if it is uneven), liquid crystal cannot be filled in every corner uniformly and accurately in the following process. However, since the application of the overcoat layer is also affected by the underlying colored pixel array, the application of the overcoat layer is likely to be uneven. This can make the surface of the overcoat layer uneven.
Despite the importance given to the management of the surface flatness (unevenness) of color resist layers and an overcoat layer constituting a color filter, there is yet no apparatus capable of inspecting the flatness (uneven application) of these layers accurately. Under present circumstances, the reliability of inspection depends on visual inspection by skilled inspectors.
As a related art document, for example, Japanese Patent Laid-Open No. 09-126948 discloses a method of inspecting scratches on, or unevenness of, the surface of a color filter. In this method, reflected light from the color filter is measured while rotating a substrate at constant or uniform speed in order to prevent a pixel edge part of the color filter from being detected as a pseudo defect. However, this publication does not disclose ways of detecting the flatness (unevenness) of the surfaces of color resist layers and an overcoat layer inherent in the pigment dispersion method.